1. Field of the Invention
The present invention relates to probes used in the electrically testing and so forth of various types of electrical and electronic components. More specifically, the present invention relates to a probe in which a rear end of a plunger, which is inserted in a cylindrical barrel so as to be capable of moving backward and forward therein, is urged by a coil spring so that a front end thereof is made to protrude from an open end of the barrel.
2. Description of the Related Art
As shown in FIG. 5, a probe 1 used in electrically testing and so forth of various types of electrical and electronic components has a configuration in which a conductive plunger 3 is inserted inside a conductive barrel 2, formed in the shape of a cylinder, so as to be capable of moving backward and forward inside the barrel 2. One end of the plunger 3 protrudes from the end of the barrel 2 so as to establish contact with terminals or the like of an object to be tested, using the end of the plunger.
In order to prevent the plunger 3 from being pulled out from the barrel 2, for example, a portion of the plunger 3 that is inserted inside the barrel 2 is formed wider than the other portions, and in addition, a diameter of an open end portion of the barrel 2 is made narrower to prevent the plunger 3 from passing through.
In order to enable the plunger 3 to make resilient contact with the terminals or the like of the object to be tested, a coil spring 4 is received inside the barrel 2 to push a rear end 3b of the plunger 3. The plunger 3 is thus urged in a direction such that a front end 3a of the plunger 3 protrudes from the barrel 2.
For electrical contact between the object to be tested and the test equipment via the probe 1, the probe 1 having the above-described structure is configured so that, first, the front end 3a of the plunger 3 makes contact with the terminals or the like of the object to be tested, and the plunger 3 makes contact with an inner wall 21 of the barrel 2, inside the barrel 2. By doing so, electrical contact is established with the test equipment via a wiring cable or the like that is connected to the barrel 2.
However, the plunger 3 is formed to have a diameter slightly smaller than the inner diameter of the barrel 2 so as to allow it to easily move backward and forward inside the barrel 2; it is thus received inside the barrel 2 with some amount of play. Accordingly, when the plunger 3 has itself swung inside the barrel 2 due to this play, the contact conditions between the outer circumference of the plunger 3 and the inner wall 21 of the barrel 2 change.
As a result, the change in the contact conditions between the inner wall of the barrel 2 and the plunger 3 causes variations in the electrical contact conditions and causes the contact conditions to deteriorate, thus affecting the electrical contact conditions, for example, the high-frequency characteristics.
In order to prevent changes in the electrical contact conditions due to the unstable contact between the plunger 3 and the barrel 2, a probe has been proposed in which the outer circumference of the plunger 3 is pressed against the inner circumference of the barrel 2 by cutting the rear end 3b of the plunger 3 on a slant, as shown in FIG. 6, and pushing the spring 4 against this inclined surface (see JP2000243500A2).
In a similar configuration in which the rear end 3b of the plunger 3 is cut at an angle, as shown in FIG. 7, a probe 1 has been proposed in which a conductive bias pin 7 is introduced between the plunger 3 and the spring 4. Not only the outer circumferential surface of the plunger 3 is pressed against the inner wall of the barrel 2, but the bias pin 7 is also brought into contact with the inner wall of the barrel 2, which improves the electrical contact conditions by increasing the contact area via the bias pin 7 (see JP200690941A2). Furthermore, as shown in FIGS. 8A and 8B, a probe 1 has been proposed in which, in order to improve the contact between the inner circumference of the barrel 2 and the outer circumference of the plunger 3, protrusions 29 and 39 are formed in the inner wall of the barrel 2 and/or in the outer circumference of the plunger 3, respectively, which increases the contact area between the two (see FIGS.6 and 7 in JP2006164660A2).
In the probes 1 in the related art, having the configuration described above, in the probe having the configuration in which the rear end 3b of the plunger 3 is cut at an angle (FIGS. 6 and 7), an axial-direction force exerted by the coil spring 4 acts, via the inclined surface, as a force that moves the plunger 3 in a direction intersecting the axis; therefore, it is possible to press the outer face of the plunger 3 against the inner wall 21 of the barrel 2 while the axial direction of the plunger 3 and the axial direction of the barrel 2 remain parallel. As a result, as shown by the x marks in FIG. 6, it is possible to establish contact between the outer circumference of the plunger 3 and the inner circumference of the barrel 2 over a relatively long distance in the longitudinal direction of the plunger 3.
However, the force acting on the plunger 3 is not only the urging force from the spring 4, but also a pressing force exerted when the front end 3a of the plunger 3 presses against the object to be tested.
Thus, when the pressing force of the object to be tested, which is exerted on the plunger 3, includes not only a component in the axial direction of the plunger 3, but also a component in a direction intersecting the axial direction, the plunger 3 swings even in the probe 1 having the above-described configuration, in which the rear end 3b of the plunger 3 is cut at an angle.
When swing of the plunger 3 occurs in this way, and the axial direction of the plunger 3 is disposed at an angle with respect to the axial direction of the barrel, as shown in FIG. 9, the outer circumference of the plunger 3 contacts the inner wall 21 of the barrel 2 at only a few points. Therefore, there is the problem described above, namely, that the contact area is drastically reduced compared to the case described with reference to FIG. 6, and the electrical resistance increases.
Moreover, in the configuration in which the bias pin 7 is provided between the coil spring 4 and the rear end 3b of the plunger 3, as shown in FIG. 7, when using such a probe 1 to test semiconductor devices or the like, it is necessary to form the bias pin 7 with a total length of about 1 mm to 2 mm. Because this bias pin 7 with such a minute size must be machined to have a complex shape, as shown in FIG. 7, high-level technology is required to machine the bias pin 7.
The increased number of parts resulting from providing the bias pin 7, combined with the fact that the parts are extremely small, makes the assembly of the probe 1 more difficult. As a result, the production efficiency of this type of probe 1 is reduced.
In addition, the difficulty of production and assembly increases the manufacturing costs of the probe, and the cost increase is thus reflected in the price, causing the price competitiveness to be reduced.
In the related art described in JP2006164660A2, when contact is established between the inner wall 21 of the barrel 2 and the outer circumference of the plunger 3 without providing protrusions, contact is established at only one point when viewed in cross section from the orthogonal direction with respect to the axis. In contrast, by providing the protrusions described above, contact occurs at multiple points. Due to the increase in contact area as a result of increasing the number of contact points in this way, it is possible to improve the electrical characteristics; for example, the electrical resistance is reduced.
However, by forming the protrusions on the outer circumference of the plunger 3 and/or on the inner circumference of the barrel 2 in this way, even though the contact area between the outer circumference of the plunger 3 and the inner circumference of the barrel 2 is increased, if the plunger 3 swings as described above, the contact area between the outer circumference of the plunger 3 and the inner circumference of the barrel 2 is drastically reduced. Therefore, an increase in the electrical resistance is unavoidable, which causes degradation of the measurement results.
Moreover, when using this probe 1 for testing semiconductor devices or the like, it is necessary to form the barrel 2 and the plunger 3, which constitute the probe 1, as comparatively minute parts. In addition, because it is necessary to form protrusions such a minute barrel and plunger, as shown in FIG. 8B, extremely high-level technology is required for their manufacture, which decreases the productivity and increases the manufacturing costs.
The present invention has been conceived in order to overcome the above-described problems with the related art. It is an object of the present invention to provide a probe which can be easily manufactured and which can effectively improve electrical contact between a plunger and a barrel with a relatively simple improvement, namely, by the addition of comparatively simple parts that can be procured at low cost, resulting in a probe with superior electrical characteristics, for example, high-frequency characteristics.